sparse file processing improvements for dd

[Pádraig Brady]

On 08/10/14 15:55, Pádraig Brady wrote:
> Subject: [PATCH 2/4] cp: avoid speculative preallocation with --sparse=always
> 
> With --sparse=always use fallocate(...PUNCH_HOLE...) to
> avoid any permanent allocation due to speculative
> preallocation employed by file systems such as XFS.

For the record, I was wondering if we should apply the same punch_hole()
processing to dd conv=sparse ?  I'm 60:40 against as the implementation
is documented to skip existing data in the output for NULs in the input.

If one really cares about minimizing allocation after a dd copy,
one can call `fallocate --dig-holes`, albeit with repeated processing
of the non holes.

cheers,
Pádraig.